Semiconductor devices in which two thyristors are connected in anti-parallel so that current can flow in both directions (hereinafter referred to as TRIACs) are known (see for example, Patent Document 1).
For example, regarding the TRIAC described in Patent Document 1, P+ regions are formed on a first surface of a semiconductor substrate on which a first electrode and a gate electrode are formed, and on a second surface of the semiconductor substrate on which a second electrode is formed. Additionally, a P++ region, which is a high concentration region, is formed so as to be included in the P+ region. In the TRIAC described in Patent Document 1, the high concentration region (P++ region) is formed, thereby making it possible to encourage a recombination of carriers and achieve an improvement of (dv/dt)c (a rate of an increase in critical off-state voltage during commutation), that is, a suppression of commutation failures. Further, in the TRIAC described in Patent Document 1, the high concentration region is formed, thereby improving the ohmic property with the electrodes and reducing the on-voltage.